A stator blade and a rotor blade used for being incorporated in a gas turbine have respectively such a structure that a blade end plate is provided at either one or both ends of the blade-shaped portion having an aerofoil shape in cross section, and is arranged to be generally orthogonal to the longitudinal direction of the blade-shaped portion. Since the stator blade and the rotor blade are made of a specified alloy with superior heat resistance, respectively, machining thereof at high accuracy is very difficult. Nevertheless, on the other hand, these blades must be machined at high accuracy. Because of such circumstances, the electrochemical machining method is finally employed for finishing a workpiece at high accuracy after the workpiece has been roughly machined to a predetermined finish-machining margin.
In the electrochemical machining method disclosed in Japanese Patent Laid-Open Publication (KOKAI) No. JP-A-05-318230, a machining electrode is divided into three parts along the longitudinal direction of a blade-shaped portion and the respective parts is mutually slidable on the slope of other parts so as to be extensible along the slope. This arrangement properly maintains a gap (machining gap) between a machined surface of a workpiece (stator blade) to be worked and the electrode by gradually extending the parts of the electrode during the electrochemical machining process. Here, the electrochemical machining is performed by flowing electrolytic solution into the machining gap while applying a voltage (normally, a direct current voltage) between the machined surface of the workpiece and the electrode. The electrolytic solution is a conductive liquid, and is generally comprised of salt water, a sodium nitrate (NaNO3) solution, and a potassium nitrate (KNO3) solution.
With the described method, in order to extend and contract the electrode in the longitudinal direction of the blade-shaped portion of the workpiece, the electrode is divided into three-parts, so that each of the three-parts may be slidable on the slope which is inclined to the machined surface of the blade-shaped portion. Namely, relatively varying a position of each part in advancing movement thereof allows each part of the electrode to be relatively moved along the slope.
As described above, since the method disclosed in Japanese Patent Laid-Open Publication (KOKAI) No. JP-A-05-318230 is to divide the electrode into the three-parts to thereby relatively move respective parts, at least two pairs of driving means for relatively moving each part of the electrode are needed. Accordingly, there occurs a problem such that the number of parts of the electrode is increased, which makes the structure complex. In addition, there is another problem such that the large number of the parts causes an increase in the size of the electrode, and therefore it is difficult to use the electrode for performing electrochemical machining of a small workpiece.